The present invention relates to ceramics for use in electrical and electronic equipment and more particularly, to ceramics having high dielectric constant and low microwave loss and stability against temperature variations for use in various microwave circuits.
Conventionally, in the microwave frequency ranges, dielectrics have been applied for impedance matching in the microwave circuits and producing dielectric resonators, etc. Particularly, with the recent progress in the technique for integration of microwave circuits, there has been a strong demand for small-sized dielectric resonators as oscillator frequency stabilizer, frequency filters, etc., and also for materials having high dielectric constant and low microwave loss with sufficient stability against temperature variations to be used, for example, as substrates for integrated circuits.
Although alumina has been generally employed as a low loss dielectric material for use as substrates, the material has disadvantages such as the fact that relative dielectric constant thereof is small at approximately 10, with a large temperature coefficient of approximately 120 to 150 ppm/.degree. C.
Meanwhile, as materials for dielectric resonators, various compositions, for example, compositions of the BaO-TiO.sub.2 group, compositions prepared by substituting other elements for part of BaO-TiO.sub.2 group, or compositions prepared by combining TiO.sub.2, whose dielectric constant has negative temperature variation rate, with dielectric compositions whose dielectric constant has a positive temperature coefficient, have been mainly employed. The compositions as described above, however, still have drawbacks such as large dielectric loss, large temperature variations with respect to the dielectric constant, large deviations in the temperature variation rate of the dielectric constant, etc., thus presenting various problems in actual use.
Accordingly, an essential object of the present invention is to provide dielectric ceramics for use in electrical and electronic equipment which are large in dielectric constant, and small in loss with respect to microwaves, with sufficient stability against temperature variations.
Another important object of the present invention is to provide dielectric ceramics of the above described type which are simple in structure and stable in functioning and can be manufactured on a large scale at low cost.
A further object of the present invention is to provide a method of manufacturing dielectric ceramics of the above described type through simple processes.
In accomplishing these and other objects, according to the present invention, a calcined material having a composition including at least two of the components 3BaO.ZnO.Nb.sub.2 O.sub.5, 3BaO.ZnO.Ta.sub.2 O.sub.5, 3BaO.MgO.Nb.sub.2 O.sub.5, and 3BaO.MgO.Ta.sub.2 O.sub.5 and produced under optimum processing conditions as disclosed, is employed for obtaining ceramics having small microwave loss with large dielectric constant and suitable for use as dielectric resonators, electrical filters, substrates, etc. with substantial elimination of disadvantages inherent in the conventional ceramics and manufacturing method therefor.